Systems and methods for multi-spacecraft distributed ascent

ABSTRACT

Example methods and systems of deploying a constellation of spacecraft are described. An example method includes releasing a cluster of spacecraft from a launch vehicle at a first orbit, separating spacecraft in the cluster of spacecraft from each other to minimize overlap of visibility periods from a ground station, and raising each of the spacecraft as separated simultaneously in a synchronized ascent to a respective final orbit. An example system includes a cluster of spacecraft in orbit at a first orbit, and a ground station in communication with spacecraft of the cluster of spacecraft when the spacecraft of the cluster are visible to the ground station. The ground station commands each spacecraft to separate from each other and to raise in altitude as separated simultaneously in a synchronized ascent to a respective final orbit.

FIELD

The present disclosure relates generally to a system for deploying aconstellation of spacecraft, and more particularly, to a procedure toseparate spacecraft deployed from a single launch vehicle from eachother in such a way that during ascent maneuvers, times that eachspacecraft is in view of a particular ground station has about minimaloverlap with times that other spacecraft deployed from the same launchvehicle are in view of the same ground station.

BACKGROUND

For many applications, a constellation of spacecraft is required.Traditionally, deployment of spacecraft constellations, such as groupsof satellites, into separate orbits requires numerous launches which canbe costly. Alternatively, if many spacecraft comprising a constellationare launched from a single launch vehicle at the same time, theproximity of the spacecraft in the constellation could increase demandon one or more ground stations. However, to reduce system complexity anddevelopment costs, it is desired to minimize the number and intricacy ofground facilities and ground support equipment.

What is needed is a strategy to minimize ground station supportcomplexity while addressing constellation initialization issues.

SUMMARY

In one example, a method of deploying a constellation of spacecraft isdescribed. The method comprises releasing a cluster of spacecraft from alaunch vehicle at a first orbit, separating spacecraft in the cluster ofspacecraft from each other to minimize overlapping visibility periodsfrom a ground station, and raising each of the spacecraft as separatedsimultaneously in a synchronized ascent to a respective final orbit.

In another example, a non-transitory computer readable storage medium isdescribed having stored therein instructions, that when executed by asystem having one or more processors, causes the system to performfunctions. The functions comprise causing spacecraft in a cluster ofspacecraft that have been released into a first orbit to separate fromeach other to minimize overlapping visibility periods from a groundstation, and causing each of the spacecraft as separated to raisesimultaneously in a synchronized ascent to a respective final orbit.

In another example, a system for deploying a constellation of spacecraftis described. The system comprises a cluster of spacecraft in orbit at afirst orbit, and a ground station in communication with spacecraft ofthe cluster of spacecraft when the spacecraft of the cluster are visibleto the ground station. The ground station sends a first command to eachspacecraft in the cluster of spacecraft indicating to separate from eachother so that relative phasing of each spacecraft to each otherminimizes overlapping visibility periods from the ground station, andafter the spacecraft have separated, the ground station sends a secondcommand to each of the spacecraft indicating to raise as separatedsimultaneously in a synchronized ascent to a respective final orbit.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments or may be combined in yetother embodiments further details of which can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE FIGURES

The novel features believed characteristic of the illustrativeembodiments are set forth in the appended claims. The illustrativeembodiments, however, as well as a preferred mode of use, furtherobjectives and descriptions thereof, will best be understood byreference to the following detailed description of an illustrativeembodiment of the present disclosure when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 illustrates a system for deploying a constellation of spacecraftis illustrated, according to an example embodiment.

FIG. 2 is a diagram illustrating a conceptual orbit motion of thespacecraft and a visibility arc (portion of the orbit) for the groundstation, according to an example embodiment.

FIG. 3 illustrates a graph showing an example visible arc length versusaltitude relative to Equatorial Ground Station, according to an exampleembodiment.

FIG. 4 is a diagram illustrating a conceptual deployment of the clusterof spacecraft, according to an example embodiment.

FIG. 5 is a diagram illustrating a conceptual orbital motion of thecluster of spacecraft, according to an example embodiment.

FIG. 6 is a diagram illustrating another conceptual orbital motion ofthe cluster of spacecraft, according to an example embodiment.

FIG. 7 is a diagram illustrating another conceptual orbital motion ofthe cluster of spacecraft, according to an example embodiment.

FIG. 8 is a diagram illustrating another conceptual orbital motion ofthe cluster of spacecraft, according to an example embodiment.

FIG. 9 is a diagram illustrating another conceptual orbital motion ofthe cluster of spacecraft, according to an example embodiment.

FIG. 10 illustrates a table showing all the spacecraft being raised to ahigher altitude, according to an example embodiment.

FIG. 11 is a diagram illustrating a conceptual orbital motion of thespacecraft, according to an example embodiment.

FIG. 12 is a diagram illustrating a conceptual visibility profile of thespacecraft from the ground station, according to an example embodiment.

FIG. 13 is a diagram illustrating another conceptual visibility profileof the spacecraft in an instance using two ground stations 180° apart,according to an example embodiment.

FIG. 14 shows a flowchart of an example method of deploying aconstellation of spacecraft, according to an example embodiment.

FIG. 15 shows a flowchart of an example method that may be used with themethod of FIG. 14, according to an example embodiment.

FIG. 16 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 17 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 18 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 19 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 20 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 21 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 22 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 23 shows a flowchart of another example method that may be usedwith the method of FIG. 14, according to an example embodiment.

FIG. 24 shows a flowchart of another example method of deploying aconstellation of spacecraft, according to an example embodiment.

FIG. 25 shows a flowchart of another example method that may be usedwith the method of FIG. 24, according to an example embodiment.

FIG. 26 shows a flowchart of another example method that may be usedwith the method of FIG. 24, according to an example embodiment.

FIG. 27 shows a flowchart of another example method that may be usedwith the method of FIG. 24, according to an example embodiment.

DETAILED DESCRIPTION

Disclosed embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which some, but not all ofthe disclosed embodiments are shown. Indeed, several differentembodiments may be described and should not be construed as limited tothe embodiments set forth herein. Rather, these embodiments aredescribed so that this disclosure will be thorough and complete and willfully convey the scope of the disclosure to those skilled in the art.

Within examples herein, a multi-spacecraft low-thrust distributed ascentstrategy is described characterized by relative phasing of eachspacecraft involved in an ascent cluster, and a final phasing of eachspacecraft within the constellation as well as ground stationconstraints associated with an applied mission. Following deployment ofthe spacecraft cluster from a launch vehicle, a method of relativespatial separation from spacecraft to spacecraft is described to createan orbit phase between the spacecraft at some staging orbit. Afterphasing of the spacecraft within the staging orbit, the constellationascends in a simultaneous fashion keeping their relative phasing.

The strategy minimizes ground support complexity and constellationinitialization complexity, such as ground asset support needs. Thestrategy performs orbit raising in a way that schedules ground contactsin a synchronized, predictable fashion, and also phases spacecraft priorto ascent into final orbit. Some solutions perform spacecraft ascentwith no regard to ground station impact, however, the examples describedherein include distributed and phased ascent of spacecraft to minimizeground support needs.

Within examples, releasing and pre-separating the spacecraft cluster ata lower orbit, and then commanding all spacecraft in the cluster to moveto a higher orbit simultaneously, where each satellite assumes adifferent final orbit from others in the constellation, achieves finalphasing as desired. This also enables multiple spacecraft comprising aconstellation to be launched together and efficiently operated on-orbit,thus reducing the total cost of the mission.

Referring now to FIG. 1, a system 100 for deploying a constellation ofspacecraft is illustrated, according to an example embodiment. Thesystem 100 includes a cluster 102 of spacecraft 104, 106, 108, and 110in orbit at a first orbit. The system 100 also includes a ground station114 in communication with spacecraft of the cluster 102 of spacecraftwhen the spacecraft 104, 106, 108, and 110 are visible to the groundstation 114.

The cluster 102 of spacecraft is shown to include four spacecraft.However, in other examples, the cluster 102 may include more or fewerspacecraft, or may include between two to about twelve or sixteenspacecraft, for example. The spacecraft 104, 106, 108, and 110 are shownto be satellites. However, in other examples, the spacecraft 104, 106,108, and 110 may include other vehicles for orbit per specific missions,and the spacecraft 104, 106, 108, and 110 can include differentcombinations of spacecraft as well depending on a specific mission.

The spacecraft 104, 106, 108, and 110 may be configured to revolvearound the Earth (or other celestial body) in respective orbits. In someexamples, the orbits of the spacecraft 104, 106, 108, and 110 may havesome inclination angle relative to an orbital plane in which the targetorbit lies.

The ground station 114 includes one or more processor(s) 116, acommunication interface 118, data storage 120, an output interface 122,a display 124, and a user interface 126 each connected to acommunication bus 128. The ground station user interface 126 may alsoinclude hardware to enable communication within the ground station 114and between the ground station 114 and other devices (not shown). Thehardware may include transmitters, receivers, and antennas, for example.

The communication interface 118 may be a wireless interface and/or oneor more wireline interfaces that allow for both short-rangecommunication and long-range communication to one or more networks or toone or more remote devices. Such wireless interfaces may provide forcommunication under one or more wireless communication protocols, suchas Bluetooth, WiFi (e.g., an Institute of Electrical and ElectronicEngineers (IEEE) 802.11 protocol), Long-Term Evolution (LTE), cellularcommunications, satellite communications, and/or other wirelesscommunication protocols. Such wireline interfaces may include Ethernetinterface, a Universal Serial Bus (USB) interface, or similar interfaceto communicate via a wire, a twisted pair of wires, a coaxial cable, anoptical link, a fiber-optic link, or other physical connection to awireline network. Thus, the communication interface 118 may beconfigured to receive input data from one or more devices, and may alsobe configured to send output data to other devices.

As an example, the communication interface 118 enables the groundstation 114 to wirelessly communicate with the spacecraft 104, 106, 108,and 110 of the cluster 102 through wireless communication links, such aswireless communication links 130, 132, and 134.

The data storage 120 may include or take the form of one or morecomputer-readable storage media that can be read or accessed by theprocessor(s) 116. The computer-readable storage media can includevolatile and/or non-volatile storage components, such as optical,magnetic, organic or other memory or disc storage, which can beintegrated in whole or in part with the processor(s) 116. The datastorage 120 is considered non-transitory computer readable media. Insome embodiments, the data storage 120 can be implemented using a singlephysical device (e.g., one optical, magnetic, organic or other memory ordisc storage unit), while in other embodiments, the data storage 120 canbe implemented using two or more physical devices.

The data storage 120 thus is a non-transitory computer readable storagemedium, and executable instructions 136 are stored thereon. Theexecutable instructions 136 include computer executable code. When theexecutable instructions 136 are executed by the processor(s) 116, theprocessor(s) 116 are caused to perform functions. Such functions aredescribed below.

The processor(s) 116 may be a general-purpose processor or a specialpurpose processor (e.g., digital signal processors, application specificintegrated circuits, etc.). The processor(s) 116 may receive inputs fromthe communication interface 118, and process the inputs to generateoutputs that are stored in the data storage 120 and output to thedisplay 124. The processor(s) 116 can be configured to execute theexecutable instructions 136 (e.g., computer-readable programinstructions) that are stored in the data storage 120 and are executableto provide the functionality of the ground station 114 described herein.

The output interface 122 outputs information to the display 124 or toother components as well. Thus, the output interface 122 may be similarto the communication interface 118 and can be a wireless interface(e.g., transmitter) or a wired interface as well.

The ground station 114 may be or include a computing device of variousforms, and can be included within a number of different computingdevices or servers, for example. In addition, components of the groundstation 114 can be separate from ground station 114 in some examples,such as the display 124 being a separate component.

Within examples, the processor(s) 116 of the ground station 114 canexecute the executable instructions 136 stored in the data storage 120to perform functions of sending a first command to each spacecraft 104,106, 108, and 110 in the cluster 102 indicating to separate from eachother so to minimize overlapping visibility periods from the groundstation (e.g., relative phasing of each spacecraft 104, 106, 108, and110 to each other can be about even from a perspective of the groundstation 114). Within examples, the ground station 114 sends the firstcommand instructing the spacecraft 104, 106, 108, and 110 in the cluster102 to increase or decrease in altitude in a sequential manner, and as arespective spacecraft changes altitude, the respective spacecrafttravels in a second orbit incurring a drift resulting in the relativephasing with respect to other spacecraft in the cluster 102. Inaddition,

Following, the processor(s) 116 of the ground station 114 can executethe executable instructions 136 stored in the data storage 120 toperform functions of sending a second command to each of the spacecraft104, 106, 108, and 110 indicating to raise as separated simultaneouslyin a synchronized ascent to a respective final orbit. For example, theground station 114 sends the second command instructing each of thespacecraft 104, 106, 108, and 110 to maneuver to the respective finalorbit and indicating when to begin the maneuver in order to achieve thesynchronized ascent and to maintain the relative phasing of eachspacecraft to each other.

FIG. 2 is a diagram illustrating a conceptual orbit motion of thespacecraft 104, 106, 108, and 110 and a visibility arc 144 for theground station 114, according to an example embodiment. The spacecraft104, 106, 108, and 110 will be injected into orbit at a first orbit 140of the Earth, and following separation and ascent, the spacecraft 104,106, 108, and 110 will arrive at a final orbit 142 of the Earth.

The ground station 114 is located on a surface of the Earth, and canonly communicate with spacecraft in orbit when the spacecraft are withinthe visibility arc 144. The visibility arc 144 corresponds to a line ofsight from the ground station 114 to the spacecraft being above thehorizon at ground station 114. Thus, the ground station 114 will only beable to communicate with spacecraft during a portion of the orbit, and ahigher orbit provides a greater amount of time in which the groundstation 114 may communicate with the spacecraft. The visibility arc 144is shown are being between visibility arcs 146 and 148, which are partsof the first and final orbits, respectively.

FIG. 3 illustrates a graph showing an example visible arc length versusaltitude relative to Equatorial Ground Station, according to an exampleembodiment. As shown, as the circular equatorial orbit altitudeincreases, the visible arc length increases as well. Thus, as mentioned,a higher orbit provides a greater amount of time in which the groundstation 114 may communicate with the spacecraft.

The ground station 114 may only be able to communicate with onespacecraft at a time. Communications between the ground station 114 andspacecraft include both uplink and downlink communications so as toreceive telemetry information (e.g., information indicating datacollected by the spacecraft), and to preform ranging (e.g., distancemeasurements to measure orbit), as well as to send commands to thespacecraft (e.g., instruct to operate heaters, turn on functions andprocesses, send instructions for executing maneuvers, etc.). Since theground station 114 communicates with the spacecraft over a directline-of-sight wireless communication link, if the cluster 102 ofspacecraft are all within the visibility arc 144 at the same time, theground station 114 may not be able to communicate with each during theperiod of orbit in which the cluster 102 is in the visibility arc 144because the ground station 114 only communicates with one spacecraft ata time.

FIG. 4 is a diagram illustrating a conceptual deployment of the cluster102 of spacecraft, according to an example embodiment. In this example,the four spacecraft 104, 106, 108, and 110 are represented. The cluster102 are released from a launch vehicle 150 at the first orbit 140. Asingle launch vehicle 150 is used, and the launch vehicle 150 may takemany forms include a spacecraft or rocket ship, for example.

The cluster 102 is deployed at a first orbit (e.g., which may becircular), and the cluster 102 moves in unison around the Earth alongthe first orbit 140. A relative phasing or spacing of each spacecraft toeach other is about 0° when seen from the ground since all spacecraftare in the same general first orbit 140 (within a distance tolerance toone another so as to avoid collisions). The spacecraft may not be in thesame exact orbit, but will be very close to within the same orbit so asto travel in orbital motion into and out of view of the ground station114 at the substantially same time.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to skill in theart, may occur in amounts that do not preclude the effect thecharacteristic was intended to provide.

FIG. 5 is a diagram illustrating a conceptual orbital motion of thecluster 102 of spacecraft, according to an example embodiment. Since allspacecraft are in the cluster 102 together, all spacecraft aresimultaneously in view of the ground station 114 at the same time whenwithin the visibility arc 144. For example, all spacecraft will comeinto view of the ground station 114 (as shown by arrow 152 with thecluster entering the visibility arc 144) at approximately the same time,and then go out of view of the ground station 114 (as shown by arrow 154with the cluster leaving the visibility arc 144) after a period of time.The time period may not be long enough to allow each spacecraft to haveenough communication time with the ground station 114.

Alternatively, efficiency can be achieved by using one ground stationwhen spacing between the spacecraft of the cluster 102 is configured ina manner so that the spacecraft come in view of the ground station 114at different times so the ground station 114 can communicate with eachspacecraft individually for a longer period of time. Thus, thespacecraft can be separated from each other so that relative phasing ofeach spacecraft to each other is about even from a perspective of theground station 114, to minimize overlapping visibility periods from theground station 114, for example. The separating, or phasing, of thespacecraft can allow the ground station 114 to communicate with eachindividually since each can be spaced apart so that about at most one iswithin the visibility arc 144 at any given time, for example. Or, thespacecraft can be separated so that a respective spacecraft is in thevisibility arc 144 long enough for communication to occur with theground station 114. Within examples described below, the spacecraft inthe cluster 102 are separated by increasing or decreasing in altitude ina sequential manner, so that as a respective spacecraft changesaltitude, the respective spacecraft travels in a second orbit incurringa drift resulting in the relative phasing with respect to otherspacecraft in the cluster 102.

FIG. 6 is a diagram illustrating another conceptual orbital motion ofthe cluster 102 of spacecraft, according to an example embodiment. InFIG. 6, a spacecraft in the cluster 102 begins a maneuver to increase ordecrease the orbit size (altitude), and therefore induce a drift ratewith respect to the spacecraft remaining in the cluster 102. Over time,the drift incurs a phasing or separation relative to the spacecraftremaining in the cluster 102. The spacecraft 104 stops the burn maneuverwhen the desired drift rate from the cluster 102 is obtained. In thisexample, a desired drift rate may result in about a phase separationangle of 90°. A resulting drift orbit 156 of the spacecraft 104 causesthe spacecraft 104 to be separated from the cluster 102.

FIG. 6 also illustrates a table showing the spacecraft 104 separated bythe cluster 102 by about 90°. This phase separation can be achieved, forexample, as shown at about the drift orbit 156 of 1,300 km. Byincreasing to a higher drift altitude, the spacecraft 104 drifts due toa larger orbit around the Earth.

FIG. 7 is a diagram illustrating another conceptual orbital motion ofthe cluster 102 of spacecraft, according to an example embodiment. InFIG. 7, the spacecraft 104 coasts as the next spacecraft 106 begins amaneuver to increase or decrease the orbit size (altitude), andtherefore induce a drift rate with respect to the spacecraft remainingin the cluster 102. Over time, the drift incurs a phasing or separationrelative to the spacecraft remaining in the cluster 102. The spacecraft106 stops the burn maneuver when the desired drift from cluster 102 isobtained. Spacecraft 106 will remain separated from spacecraft 104. Anamount of separation will be controlled by an amount of time elapsedbetween a start of maneuvering of spacecraft 104 and a start ofmaneuvering of spacecraft 106.

FIG. 7 also illustrates a table showing the spacecraft 106 separated bythe spacecraft 104 by about 90°. This phase separation can be achieved,for example, as shown at about the drift altitude of 1,300 km. Byincreasing to a higher drift altitude, the spacecraft 106 drifts due toa larger orbit around the Earth and may now be in the same orbit as thespacecraft 104.

FIG. 8 is a diagram illustrating another conceptual orbital motion ofthe cluster 102 of spacecraft, according to an example embodiment. InFIG. 8, the spacecraft 104 and 106 coast as the next spacecraft 108begins a maneuver to increase or decrease the orbit size (altitude), andtherefore induce a drift rate with respect to the spacecraft remainingin the cluster 102. The spacecraft 108 stops the burn maneuver when thedesired drift from cluster 102 is obtained. Spacecraft 108 will remainseparated from spacecraft 106 and spacecraft 104. An amount ofseparation will be controlled by an amount of time elapsed between astart of maneuvering of spacecraft 108 and a start of maneuvering ofspacecraft 106.

FIG. 8 also illustrates a table showing the spacecraft 108 separated byabout 90°. This phase separation can be achieved, for example, as shownat about the drift altitude of 1,300 km. By increasing to a higher driftaltitude, the spacecraft 108 drifts due to a larger orbit around theEarth and may now be in the same orbit as the spacecraft 104 and thespacecraft 106.

FIG. 9 is a diagram illustrating another conceptual orbital motion ofthe cluster 102 of spacecraft, according to an example embodiment. InFIG. 9, the spacecraft 104, 106, and 108 coast as the next spacecraft110 begins a maneuver to increase or decrease the orbit size (altitude),and therefore reduce the drift rate difference with respect to,spacecraft 104, 106, and 108. Spacecraft 110 will remain separated fromspacecraft 108, spacecraft 106 and spacecraft 104. An amount ofseparation will be controlled by an amount of time elapsed between astart of maneuvering of spacecraft 110 and a start of maneuvering ofspacecraft 108.

FIG. 9 also illustrates a table showing all the spacecraft 104, 106,108, and 110 separated by about 90°. This phase separation can beachieved, for example, as shown at about the drift altitude of 1,300 km.

The specific amount of phase separation may be based on how manyspacecraft are included in the cluster 102 so that after all spacecraftare separated, only one spacecraft is visible to the ground station 114at any given time. In one example, the separation phase is about 360/x,where x is a number of spacecraft in the cluster 102. Thus, spacing canbe even around the Earth within some tolerance to distribute load on theground station 114 so that the ground station 114 can do more for eachspacecraft (and minimize idle times of ground station 114, for example).

As one example, with sixteen spacecraft, spacing is 360/16 enabling 1/16orbit time for the ground station 114 to work with each individualspacecraft and communicate with each individual spacecraft when thespacecraft is visible (e.g., to allow enough time for antenna pointing,configuration, ranging, communications and data processing to occur asneeded for the ground station 114, and after that do the same for thenext spacecraft, and so on). Example communications that the groundstation 114 performs includes assessing health of the spacecraft, aswell as providing commands for operations that the spacecraft is toperform.

Following separation, each of the spacecraft 104, 106, 108, and 110 israised, as separated, simultaneously in a synchronized ascent to theirrespective final orbits. Thus, the separation can be achieved by raisingall the spacecraft by a small amount (e.g., 1000 km to 1400 km)sequentially to provide phasing (separation) at a lower orbit, and thena timed simultaneous ascent of all spacecraft 104, 106, 108, and 110results in the spacecraft 104, 106, 108, and 110 arriving at their finalorbits retaining the desired separation. The final orbit may be muchhigher, such as between about 2,400 km to 45,000 km or higher.

FIG. 10 illustrates a table showing all the spacecraft 104, 106, 108,and 110 being raised to a higher altitude, according to an exampleembodiment. For example, as the last spacecraft 110 approaches the driftaltitude, all the spacecraft 104, 106, 108, and 110 begin theirpre-loaded burn to simultaneously maneuver from about the same startingdrift orbit 156 with 90° phase separation from each other. The groundstation 114 may send a timed command to each of the spacecraft 104, 106,108, and 110, when visible to the ground station 114, indicating when tomaneuver to the respective final orbit. The ground station 114individually commands the spacecraft 104, 106, 108, and 110 to separateand then raise in altitude. The timed command indicates when to beginthe maneuver (e.g., a start time) in order to achieve the synchronizedascent and to maintain the relative phasing of each spacecraft to eachother.

The simultaneous raising of each of the spacecraft 104, 106, 108, and110 occurs starting from about a same starting altitude (e.g., the driftorbit 156), which is higher or lower than the first orbit 140, with therelative phasing separating each of the spacecraft to each otherresulting in the relative phasing remaining in place once each of thespacecraft arrives at the respective final orbit 142.

The final orbit 142 may be the same for all spacecraft 104, 106, 108,and 110, or each spacecraft may have a separate final orbit depending onan applicable mission.

FIG. 11 is a diagram illustrating a conceptual orbital motion of thespacecraft 104, 106, 108, and 110, according to an example embodiment. Asimultaneous burn of all the spacecraft 104, 106, 108, and 110 resultsin a synchronized ascent with all the spacecraft 104, 106, 108, and 110separated in phase (e.g., 90°). This results in a desired phasing orseparation at the final orbit 142. In addition, this creates spacingbetween the spacecraft 104, 106, 108, and 110 from a perspective of theground station 114 to enable a manageable and predictable visibilitytime frame at the ground station 114 as the constellation of spacecraftascends to the final orbit 142.

FIG. 12 is a diagram illustrating a conceptual visibility profile of thespacecraft 104, 106, 108, and 110 from the ground station 114, accordingto an example embodiment. As shown in FIG. 12, over time, eachspacecraft comes into and out of view of the ground station 114 in apattern due to the orbital motion and spacing between the spacecraft104, 106, 108, and 110.

FIG. 13 is a diagram illustrating another conceptual visibility profileof the spacecraft 104, 106, 108, and 110 in an instance using two groundstations 180° apart in longitude, according to an example embodiment. Asshown in FIG. 13, the solid line rectangles represent spacecraft in viewof a first ground station and the dotted line rectangles representspacecraft in view of the second ground station. Again, over time, eachspacecraft comes into and out of view of the ground stations in apattern due to the orbital motion and spacing between the spacecraft104, 106, 108, and 110.

FIG. 14 shows a flowchart of an example method of deploying aconstellation of spacecraft, according to an example embodiment. Method200 shown in FIG. 14 presents an embodiment of a method that could beused with the system 100 shown in FIG. 1, for example, or the groundstation 114. Further, devices or systems may be used or configured toperform logical functions presented in FIG. 14. In some instances,components of the devices and/or systems may be configured to performthe functions such that the components are actually configured andstructured (with hardware and/or software) to enable such performance.In other examples, components of the devices and/or systems may bearranged to be adapted to, capable of, or suited for performing thefunctions, such as when operated in a specific manner. Method 200 mayinclude one or more operations, functions, or actions as illustrated byone or more of blocks 202-206. Although the blocks are illustrated in asequential order, these blocks may also be performed in parallel, and/orin a different order than those described herein. Also, the variousblocks may be combined into fewer blocks, divided into additionalblocks, and/or removed based upon the desired implementation.

It should be understood that for this and other processes and methodsdisclosed herein, flowcharts show functionality and operation of onepossible implementation of present embodiments. In this regard, eachblock may represent a module, a segment, or a portion of program code,which includes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process. Theprogram code may be stored on any type of computer readable medium ordata storage, for example, such as a storage device including a disk orhard drive. Further, the program code can be encoded on acomputer-readable storage media in a machine-readable format, or onother non-transitory media or articles of manufacture. The computerreadable medium may include non-transitory computer readable medium ormemory, for example, such as computer-readable media that stores datafor short periods of time like register memory, processor cache andRandom Access Memory (RAM). The computer readable medium may alsoinclude non-transitory media, such as secondary or persistent long termstorage, like read only memory (ROM), optical or magnetic disks,compact-disc read only memory (CD-ROM), for example. The computerreadable media may also be any other volatile or non-volatile storagesystems. The computer readable medium may be considered a tangiblecomputer readable storage medium, for example.

In addition, each block in FIG. 14, and within other processes andmethods disclosed herein, may represent circuitry that is wired toperform the specific logical functions in the process. Alternativeimplementations are included within the scope of the example embodimentsof the present disclosure in which functions may be executed out oforder from that shown or discussed, including substantially concurrentor in reverse order, depending on the functionality involved, as wouldbe understood by those reasonably skilled in the art.

At block 202, the method 200 includes releasing the cluster 102 ofspacecraft from the launch vehicle 150 at the first orbit 140. Withinexamples, after releasing the cluster 102 of spacecraft from the launchvehicle 150 at the first orbit 140, relative phasing of each spacecraftto each other is about zero degrees

At block 204, the method 200 includes separating spacecraft in thecluster 102 of spacecraft from each other to minimize overlappingvisibility periods from the ground station 114. This can include, forexample, separating the spacecraft in the cluster 102 so that relativephasing of each spacecraft to each other is about even from aperspective of the ground station 114. The separation occurs in asequential manner, and as a respective spacecraft changes altitude, therespective spacecraft travels in a second orbit incurring a driftresulting in the relative phasing with respect to other spacecraft inthe cluster 102, for example. In addition, in some examples, theseparation occurs such that only one spacecraft is visible to the groundstation 114 at any given time to reduce cost by having and using onlyone ground station at a time.

At block 206, the method 200 includes raising each of the spacecraft asseparated simultaneously in a synchronized ascent to a respective finalorbit 142. The ground station 114 can send a timed command to each ofthe spacecraft, when visible to the ground station 114, indicating tomaneuver to the respective final orbit 142. The timed command mayindicate a start time for the simultaneous ascent. Thus, each of thespacecraft 104, 106, 108, and 110 can be simultaneously raised fromabout a same starting altitude (e.g., the drift orbit 156), higher orlower than the first orbit 140, with the relative phasing separatingeach of the spacecraft to each other resulting in the relative phasingremaining once each of the spacecraft arrives at the respective finalorbit 142.

The ground station 114 is positioned on a surface of Earth andcommunicates with each spacecraft via a line-of-sight communication andcommunicates with each spacecraft one at a time. Thus, the groundstation 114 individually commands the spacecraft 104, 106, 108, and 110to separate and then raise. This method avoids the need for many groundstations to reduce cost of the system 100.

The method 200 may take a month, 6 months, a year, etc. to complete thefull separation and ascent of the spacecraft to the final orbit 142depending on an altitude of the first orbit 140, and altitude of thefinal orbit 142, a mass of the spacecraft and other factors to consider.

FIG. 15 shows a flowchart of an example method that may be used with themethod 200 of FIG. 14, according to an example embodiment. As shown atblock 208, additional functions can include causing the spacecraft inthe cluster 102 to increase or decrease in altitude in a sequentialmanner, and as a respective spacecraft changes altitude, the respectivespacecraft travels in a second orbit 156 incurring a drift resulting inthe relative phasing with respect to other spacecraft in the cluster102.

FIG. 16 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 210, additional functions can include causing a firstspacecraft in the cluster 102 to increase or decrease in altitudeincurring a drift due to being in a different orbit, and as shown atblock 212, further additional functions can include causing the firstspacecraft in the cluster 102 to stop the change in altitude, once adesired drift rate with respect to other spacecraft in the cluster 102results, and to travel in a second orbit larger or smaller than thefirst orbit 140.

FIG. 17 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 214, additional functions can include separating thespacecraft such that only one spacecraft is visible to the groundstation at any given time.

FIG. 18 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 216, additional functions can include separating thespacecraft in the cluster 102 relative to each other to cause aseparation phase from spacecraft to spacecraft.

FIG. 19 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 218, additional functions can include sending a timedcommand to each of the spacecraft, when visible to the ground station114, indicating to maneuver to the respective final orbit 142, and thetimed command indicates when to begin the maneuver in order to achievethe synchronized ascent and to maintain the relative phasing of eachspacecraft to each other.

FIG. 20 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 220, additional functions can include sending eachspacecraft a start time for the synchronized ascent.

FIG. 21 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 222, additional functions can include simultaneouslyraising each of the spacecraft from about a same starting orbit,different than the first orbit 140, with the relative phasing separatingeach of the spacecraft to each other resulting in the relative phasingremaining once each of the spacecraft arrives at the respective finalorbit 142.

FIG. 22 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 224, additional functions can include communicating witheach spacecraft via a line-of-sight communication, and as shown at block226, further additional functions can include communicating with eachspacecraft one at a time.

FIG. 23 shows a flowchart of another example method that may be usedwith the method 200 of FIG. 14, according to an example embodiment. Asshown at block 228, additional functions can include the ground station114 individually commanding the spacecraft to separate and then raise.

FIG. 24 shows a flowchart of another example method of deploying aconstellation of spacecraft, according to an example embodiment. Method229 shown in FIG. 24 presents an embodiment of a method that could beused with the ground station 114 to control operation of the spacecraft104, 106, 108, and 110. Referring back to FIG. 1, the data storage 120(or non-transitory computer readable storage medium) has stored thereinthe executable instructions 136, that when executed by the processor(s)116, causes the ground station 114 to perform functions. Such functionsinclude, as shown at block 230, causing spacecraft in the cluster 102that have been released into a first orbit 140 to separate from eachother to minimize overlapping visibility periods from a ground station114, and as shown at block 232, causing each of the spacecraft asseparated to raise simultaneously in a synchronized ascent to arespective final orbit 142.

FIG. 25 shows a flowchart of another example method that may be usedwith the method 229 of FIG. 24, according to an example embodiment. Asshown at block 234, additional functions can include causing a releaseof the cluster of spacecraft from the launch vehicle 150 at the firstorbit 140 by sending a command to the launch vehicle to release thecluster of spacecraft.

FIG. 26 shows a flowchart of another example method that may be usedwith the method 229 of FIG. 24, according to an example embodiment. Asshown at block 236, additional functions can include sending a commandto each of the spacecraft in the cluster 102 to change in altitude in asequential manner, and as a respective spacecraft changes altitude, therespective spacecraft travels in a second orbit 156 incurring a driftresulting in the relative phasing with respect to other spacecraft inthe cluster 102.

FIG. 27 shows a flowchart of another example method that may be usedwith the method 229 of FIG. 24, according to an example embodiment. Asshown at block 238, additional functions can include sending a commandto each spacecraft indicating a start time for the synchronized ascent.

Thus, the ground station 114 can perform these functions by sendingcommands to each of the spacecraft in the cluster 102 to increase ordecrease in altitude in a sequential manner, and sending commands toeach spacecraft indicating a start time for the synchronized ascent, forexample. The commands can be sent wirelessly through satellite links orthrough direct wireless communication, for example.

The ground station 114 can send commands at appropriate times to thespacecraft, when the spacecraft are visible to the ground station 114.For example, once a first spacecraft is separated from the cluster 102 adesired amount of distance, the ground station 114 sends a command to asecond spacecraft to initiate spacing separation, and so on. The groundstation 114 further provides commands to all spacecraft indicating whento begin the synchronized ascent. The synchronized ascent command can besent to each spacecraft when the spacecraft is in view of the groundstation 114, and provided via a timer for a future ascent initiationsuch that the ascent will begin once all spacecraft have been commandedand are offset by the desired distances. The ascent command is providedahead of time since not all spacecraft will be in view of the groundstation 114 to receive the command.

The description of the different advantageous arrangements has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different advantageousembodiments may describe different advantages as compared to otheradvantageous embodiments. The embodiment or embodiments selected arechosen and described in order to best explain the principles of theembodiments, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A method (200) of deploying a constellation ofspacecraft, the method comprising: releasing (202) a cluster (102) ofspacecraft (104, 106, 108, 110) from a launch vehicle (150) at a firstorbit (140); separating (204) spacecraft in the cluster of spacecraftfrom each other to minimize overlapping visibility periods from a groundstation (114); and raising (206) each of the spacecraft as separatedsimultaneously in a synchronized ascent to a respective final orbit(142).
 2. The method of claim 1, wherein after releasing the cluster ofspacecraft from the launch vehicle at the first orbit, relative phasingof each spacecraft to each other is about zero degrees.
 3. The method ofclaim 1, wherein separating spacecraft in the cluster of spacecraft fromeach other comprises: causing the spacecraft in the cluster to increaseor decrease in altitude in a sequential manner, wherein as a respectivespacecraft changes altitude, the respective spacecraft travels in asecond orbit (156) incurring a drift resulting in the relative phasingwith respect to other spacecraft in the cluster.
 4. The method of claim1, wherein separating spacecraft in the cluster of spacecraft from eachother comprises: causing a first spacecraft in the cluster to increaseor decrease in altitude incurring a drift due to being in a differentorbit; and causing the first spacecraft in the cluster to stop thechange in altitude, once a desired drift rate with respect to otherspacecraft in the cluster results, and to travel in a second orbitlarger or smaller than the first orbit.
 5. The method of claim 1,wherein separating spacecraft in the cluster of spacecraft from eachother comprises: separating the spacecraft such that only one spacecraftis visible to the ground station at any given time.
 6. The method ofclaim 1, wherein separating spacecraft in the cluster of spacecraft fromeach other comprises: separating the spacecraft in the cluster relativeto each other to cause a separation phase from spacecraft to spacecraft.7. The method of claim 6, wherein the separation phase is about 360/x,where x is a number of spacecraft in the cluster.
 8. The method of claim1, wherein raising each of the spacecraft as separated simultaneously inthe synchronized ascent to the respective final orbit comprises: sendinga timed command to each of the spacecraft, when visible to the groundstation, indicating to maneuver to the respective final orbit, whereinthe timed command indicates when to begin the maneuver in order toachieve the synchronized ascent and to maintain the relative phasing ofeach spacecraft to each other.
 9. The method of claim 1, wherein raisingeach of the spacecraft as separated simultaneously in the synchronizedascent to the respective final orbit comprises: sending each spacecrafta start time for the synchronized ascent.
 10. The method of claim 1,wherein raising each of the spacecraft as separated simultaneously inthe synchronized ascent to the respective final orbit comprises:simultaneously raising each of the spacecraft from about a same startingorbit, different than the first orbit, with the relative phasingseparating each of the spacecraft to each other resulting in therelative phasing remaining once each of the spacecraft arrives at therespective final orbit.
 11. The method of claim 1, wherein the groundstation is positioned on a surface of Earth and the method furthercomprises: communicating with each spacecraft via a line-of-sightcommunication; and communicating with each spacecraft one at a time. 12.The method of claim 1, wherein separating the spacecraft in the clusterof spacecraft and raising each of the spacecraft as separatedsimultaneously in the synchronized ascent comprises: the ground stationindividually commanding the spacecraft to separate and then raise. 13.The method of claim 1, wherein the cluster of spacecraft comprisesbetween two to about twelve spacecraft.
 14. A non-transitory computerreadable storage medium (120) having stored therein instructions (136),that when executed by a system (114) having one or more processors(116), causes the system to perform functions comprising: causingspacecraft in a cluster (102) of spacecraft (104, 106, 108, 110) thathave been released into a first orbit (140) to separate from each otherto minimize overlapping visibility periods from a ground station (114);and causing each of the spacecraft as separated to raise simultaneouslyin a synchronized ascent to a respective final orbit (142).
 15. Thenon-transitory computer readable storage medium of claim 14, wherein thefunctions further comprise: causing a release of the cluster ofspacecraft from a launch vehicle (150) at the first orbit (140) bysending a command to the launch vehicle to release the cluster ofspacecraft.
 16. The non-transitory computer readable storage medium ofclaim 14, wherein causing spacecraft in the cluster of spacecraft toseparate from each other comprises: sending a command to each of thespacecraft in the cluster to change in altitude in a sequential manner,wherein as a respective spacecraft changes altitude, the respectivespacecraft travels in a second orbit incurring a drift resulting in therelative phasing with respect to other spacecraft in the cluster. 17.The non-transitory computer readable storage medium of claim 14, whereincausing each of the spacecraft as separated to raise simultaneously inthe synchronized ascent to the respective final orbit comprises: sendinga command to each spacecraft indicating a start time for thesynchronized ascent.
 18. A system (100) for deploying a constellation ofspacecraft, the system comprising: a cluster (102) of spacecraft (104,106, 108, 110) in orbit at a first orbit (140); and a ground station(114) in communication with spacecraft of the cluster of spacecraft whenthe spacecraft of the cluster are visible to the ground station, whereinthe ground station sends a first command to each spacecraft in thecluster of spacecraft indicating to separate from each other so thatrelative phasing of each spacecraft to each other minimizes overlappingvisibility periods from the ground station, and the ground station sendsa second command to each of the spacecraft indicating to raise asseparated simultaneously in a synchronized ascent to a respective finalorbit (142).
 19. The system of claim 18, wherein the ground stationsends the first command instructing the spacecraft in the cluster tochange in altitude in a sequential manner, wherein as a respectivespacecraft changes in altitude, the respective spacecraft travels in asecond orbit incurring a drift resulting in the relative phasing withrespect to other spacecraft in the cluster.
 20. The system of claim 18,wherein the ground station sends the second command instructing each ofthe spacecraft to maneuver to the respective final orbit and indicatingwhen to begin the maneuver in order to achieve the synchronized ascentand to maintain the relative phasing of each spacecraft to each other.